<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<img src="images/jd1.png" alt="" id="pic"/>
<script>
    //事件源：   被触发者  img
    var pic = document.getElementById("pic");
    pic.onmouseover = function(){
        pic.onmouseout = function(){
            pic.src = "images/jd1.png";
        }
        pic.src = "images/jd2.png";
    }
</script>
</body>
</html>